Mechanical Casing Exit Window Locator and Whipstock Alignment System

ABSTRACT

A whipstock assembly for emplacing and orienting a whipstock within a wellbore. The whipstock assembly includes a whipstock, an anchor sub for securing the whipstock within the wellbore and a locating tool which is releasably secured to the whipstock. The locating tool includes a tool body with an inclined contact face and a hook which extends radially outwardly from the tool body. The hook is shaped and sized to engage a lower end of the casing exit window to align and orient the whipstock with the casing exit window.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates generally to devices and methods for steering or diverting subterranean drilling arrangements. More particularly, the invention relates to devices and method for deflecting the drilling direction of a drill string through a borehole wall and into a radial direction away from a main bore.

2. Description of the Related Art

To enhance recovery of subterranean oil and gas, it is a common practice to steer or divert a portion of a wellbore away from a substantially vertical main bore and into a horizontal or deviated lateral direction. To do this, it is typical to anchor a whipstock into the vertical wellbore and thereafter mill away a window in the casing of the wellbore. Then the milling tool is removed from the wellbore. A drill string can then be disposed into the wellbore and the drill bit deflected radially by the whipstock to form a lateral bore which extends away from the main vertical wellbore. Wellbores with a lateral bore of this type are often referred to as lateral wells.

At times, a wellbore can be temporarily abandoned with equipment and tools removed from it. For lateral wells, this would mean removal of the whipstock and its anchor. To reestablish operations in the wellbore, drilling tools must be run into the wellbore once more. This operation can be problematic, particularly when running in an anchoring a new whipstock. Even slight misalignment of the upper end of the whipstock with the lower end of the casing window can result in a subsequently run drilling string becoming hung up or fail to properly enter the lateral bore. Current methods of re-entry for emplacing the whipstock rely on a casing profile to anchor the whipstock at a desired location. However, the casing profile may be inaccurate or lack sufficient detail to be able to properly place the whipstock. In other instances, a bent sub casing or tubing is used to enter a lateral leg. However, with this technique, it can be difficult to know whether the casing or tubing is located within the lateral leg or the main bore.

SUMMARY OF THE INVENTION

The invention provides improved systems and methods for emplacing and mechanically orienting a whipstock within a wellbore having a casing exit window and lateral bore which were previously formed. A whipstock assembly is described which includes a bottom hole assembly having a whipstock and an affixed anchor sub. The whipstock presents an upper inclined contact face which will be aligned and oriented with a lower end of the casing exit window. In addition, the bottom hole assembly includes a locating tool which is releasably secured to the whipstock. In described embodiments, the locating tool includes a tool body with an angled contact face which is shaped and sized to abut and contact the upper inclined contact face of the whipstock in a complementary manner. A hook projects radially outwardly from the tool body and is shaped and sized to engage a lower end of the casing window. The hook may be fixed or radially extendable and retractable.

In operation, the whipstock assembly is run into a lateral wellbore which includes a generally vertical wellbore and at least one lateral bore. During run-in, the locating tool is angularly oriented within the wellbore so that the hook is aligned with the portion of the vertical wellbore which includes the casing exit window. The whipstock assembly is lowered within the wellbore until the hook engages the lower end of the casing exit window, stopping downward movement. At this point, the whipstock anchor is set within the wellbore. Next, the locating tool is released from the whipstock and withdrawn from the wellbore. The whipstock will be anchored within the wellbore so that its upper end is properly aligned with the lower end of the casing window. Thereafter, a drilling string can be run into the wellbore and diverted by the whipstock into the lateral bore.

BRIEF DESCRIPTION OF THE DRAWINGS

For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein:

FIG. 1 is a side, cross-sectional view of an exemplary lateral wellbore into which a whipstock assembly in accordance with the present invention is being run in.

FIG. 2 is a side, cross-sectional view of the wellbore and whipstock assembly of FIG. 1, now with the whipstock assembly having engaged the lower end of the casing window.

FIG. 3 is a side, cross-sectional view of the wellbore and whipstock assembly of FIGS. 1-2 now with the anchor for the whipstock set.

FIG. 4 is a side, cross-sectional view of the wellbore and whipstock assembly of FIGS. 1-3, now with the running tool released from the whipstock.

FIG. 5 is a side, cross-sectional view of the wellbore of FIGS. 1-4, now with a drilling string being run into the lateral leg.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts an exemplary wellbore 10 which has been drilled through the earth 12 from the surface 14. The wellbore 10 is lined with metallic casing 16. A casing exit window 18 has been cut within the casing 16 and a lateral leg 20 which extends radially away from the central, substantially vertical main bore 22 of the wellbore 10. It is noted that the wellbore 10 is a lateral wellbore which was previously abandoned and, as a result, the whipstock and anchor which were present therein have been removed.

In FIG. 1, a whipstock assembly, generally indicated at 24, is being run into the wellbore 10 from the surface 14. The whipstock assembly 24 includes a running string 26 and a bottom hole assembly 28. An axial flowbore 29 (shown in FIG. 1) is defined within the bottom hole assembly 28. The axial flowbore 29 will be aligned with the central flowbore of the running string 26 so that fluid can be pumped down from the surface 14 and through the bottom hole assembly 28. In certain embodiments, the running string 26 is coiled tubing. However, the running string 26 might also be made up of conventional tubular sections which are interconnected in an end-to-end fashion. The running string 26 will define a central flowbore along its length, as is known in the art.

The bottom hole assembly 28 includes an anchor sub 30 which is affixed to the lower end of a whipstock 32. The bottom hole assembly 28 also includes a locating tool 34 which is releasably secured to the whipstock 32. The whipstock 32 presents an upper inclined landing surface 36.

The anchor sub 30 is moveable between an unset position, wherein the anchor sub 30 and the affixed whipstock 32 are not anchored within the wellbore 10, and a set position, wherein the anchor sub 30 and the affixed whipstock 32 are anchored within the wellbore 10. In currently preferred embodiments, the anchor sub 30 features an elastomeric packer element 38 which is radially expandable to set the bottom hole assembly 28 within the main bore 22 of the wellbore 10. Also in preferred embodiments, the packer element 38 is an inflatable packer element which can be inflated by fluid which is pumped in from surface 14. In certain embodiments, a ball or plug (not shown) is landed upon a ball seat within the anchor sub 30 to divert fluid into the packer element and inflate it. A suitable inflatable packer device for use as the anchor sub 30 is the external casing packer which is described in detail in U.S. Pat. No. 5,615,741 entitled “Packer Inflation System.” U.S. Pat. No. 5,615,741 is owned by the assignee of the present application and is herein incorporated by reference.

The locating tool 34 may be releasably secured to the whipstock 32 using any number of methods which are known in the art. The locating tool 34 and whipstock 32 may be releasably secured to one another using one or more frangible members, such as shear screws, which will rupture upon application of a predetermined level of shear force. Alternatively, a collet connection, of a type known in the art, could be used to releasably interconnect the two components. This type of connection would release upon application of a predetermined level of shear force as well. In certain embodiments, the locating tool 34 and whipstock 32 are releasably secured to each other using the releasable connection that is used in Baker Hughes' Open Hole Whipstock System. This releasable connection uses a combination of collets, shear pins and a drop ball to releasably secure the components together.

The locating tool 34 includes a tool body 38 which is generally cylindrical and presents an upper end 40 which allows connection to the running string 26. Typically, the upper end 40 will have a threaded connection, of a type known in the art. The lower end of the locating tool body 38 presents an angled contact face 42 which is shaped and sized to abut and contact the inclined landing surface 36 of the whipstock 28 in a complementary manner. A hook 44 projects radially outwardly from a lateral side of the locating tool 34. The hook 44 is shaped and sized to engage a lower end 46 of the casing window 18. In preferred embodiments, the hook 44 is radially moveable inwardly and outwardly with respect to the tool body 38. In other embodiments, the hook 44 is fixed and does not move radially inwardly and outwardly.

In operation, the whipstock assembly 24 is run into the wellbore 10 in the direction of arrow 50 in FIG. 1. It is noted that, when running in, the locating tool 34 is angularly oriented within the wellbore 10 so that the hook 44 is aligned with the portion of the wellbore 10 which includes the casing exit window 18. When the whipstock assembly 24 reaches the position shown in FIG. 2, the hook 44 engages the lower end 46 of the casing window 18. In this position, the inclined contact face 36 will be properly aligned with the lower end 46 of the casing exit window 18. The whipstock 32 is aligned with the casing exit window 18 for re-entry operations by using the actual window as the datum point rather than a casing profile. Thereafter, the anchor sub 30 is set within the wellbore 10 to anchor the whipstock 32 in place (FIG. 3). Next, the locating tool 34 is released from the whipstock 32 (FIG. 4) and the running string 26 and locating tool 34 are withdrawn from the wellbore 10. Next, a drilling string 52 (FIG. 5) can be run into the wellbore 10 and be deflected by the inclined contact surface 36 of the whipstock 32 through the casing exit window 18 and into the lateral leg 20.

Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof. 

What is claimed is:
 1. A whipstock assembly for orienting and aligning a whipstock with a casing exit window in a wellbore, the whipstock assembly comprising: a whipstock for diverting a drilling string through the casing exit window; a locating tool which is releasably affixed to the whipstock, the locating tool having a tool body that is securable to a running string for running into the wellbore; and a hook which extends radially outwardly from the tool body of the locating tool, the hook being shaped and sized to engage a lower end of the casing exit window.
 2. The whipstock assembly of claim 1 further comprising: an anchor sub affixed to the whipstock, the anchor sub being moveable between an unset position, wherein the anchor sub and whipstock are not anchored within the wellbore, and a set position, wherein the anchor sub and whipstock are anchored within the wellbore.
 3. The whipstock assembly of claim 1 wherein the hook is radially moveable inwardly and outwardly with respect to the tool body.
 4. The whipstock assembly of claim 3 wherein the hook is biased radially outwardly by a resilient spring.
 5. The whipstock assembly of claim 2 wherein the anchor sub comprises an inflatable packer device.
 6. The whipstock assembly of claim 1 wherein the tool body of the locating tool presents an angled contact face which is shaped and sized to abut and contact an inclined landing surface of the whipstock in a complementary manner.
 7. A whipstock assembly for orienting and aligning a whipstock with a casing exit window in a wellbore, the whipstock assembly comprising: a whipstock having an inclined contact surface for diverting a drilling string through the casing exit window; a locating tool which is releasably affixed to the whipstock, the locating tool having a tool body that is securable to a running string for running into the wellbore; and a hook which extends radially outwardly from the tool body of the locating tool, the hook being shaped and sized to engage a lower end of the casing exit window.
 8. The whipstock assembly of claim 7 further comprising: an anchor sub affixed to the whipstock, the anchor sub being moveable between an unset position, wherein the anchor sub and whipstock are not anchored within the wellbore, and a set position, wherein the anchor sub and whipstock are anchored within the wellbore.
 9. The whipstock assembly of claim 7 wherein the hook is radially moveable inwardly and outwardly with respect to the tool body.
 10. The whipstock assembly of claim 9 wherein the hook is biased radially outwardly by a resilient spring.
 11. The whipstock assembly of claim 7 wherein the anchor sub comprises an inflatable packer device.
 12. The whipstock assembly of claim 7 wherein the tool body of the locating tool presents an angled contact face which is shaped and sized to abut and contact the inclined landing surface of the whipstock in a complementary manner.
 13. A method of installing a whipstock within a wellbore having a main bore and a lateral bore which extends radially away from the main bore, the method comprising the steps of: disposing into the wellbore a whipstock assembly having a whipstock releasably secured to a locating tool, the locating tool having a tool body and a hook which extends radially outwardly from the tool body, the hook being shaped and sized to engage a lower end of a casing exit window; engaging the lower end of the casing exit window with the hook; and releasing the locating tool from the whipstock.
 14. The method of claim 13 wherein the whipstock assembly further comprises an anchor sub affixed to the whipstock, the anchor sub being moveable between an unset position wherein the anchor sub is not anchored within the wellbore, and a set position, wherein the anchor sub is anchored within the wellbore; and further comprising the step of setting the anchor sub within the wellbore after the hook has engaged the lower end of the casing exit window.
 15. The method of claim 13 wherein the step of engaging the lower end of the casing exit window with the hook aligns an inclined contact face of the whipstock with the lower end of the casing window. 